Our results show for the first time that Abi1 is overexpressed at the invasive edge of colorectal carcinomas that display an aggressive phenotype; furthermore, phosphorylated Abi1 as well as Cortactin localize to foci of matrix degradation in the tumour cell periphery, while treatment with STI571 leads to a depletion of Y435-phosphorylated Abi1 in this compartment and suppresses tumour cell attachment to fibronectin as well as ECM degradation and tumour cell invasion in vitro. The gene discussed is FN1; the disease is colorectal carcinoma.